Well pumping apparatus



May 30, 1939. c. N. SCOTT 2,160,291

WELL PUMPING APPARATUS Filed June 1, 1937 -2 Sheets-Sheet 1 C Z arrzce N. 5602? INVENTOR,

ATTORNEYS.

May 30, 1939. I TT WELL PUMPING APPARATUS 2 Sheets-Sheet 2 III I I Iii VIIA'I'" l ii iaaaanna 5 Zarnce AL'cozf Filed June 1, 1937 INVENTOR. Adm

ATTORNEYS.

- Patented Ma 30, 1 9

"UNITED STATES PATENT OFFICE 2,160,291 WEILTUMPING APPARATUS Clarence N. Scott, Houston, Tex. Application June 1, 1931, Serial No. 145, 93 6 claims; (01. 103-52 My invention relates to the operation of bored wells equipped with pumping apparatus for raising the fluid from the pumping depth in the well to the surface of the ground. I

The fluid is caused to flow from the producing formation into the lower part ofthe well bore or 'cavity'by removing from the wllthe liquid and gas by natural or artificial means, thus reducing pressure in, or removing it almost entirely from,

10 the well bore or cavity and the adjacent producing' formation. This enables superior fluid pres sure in the outlying producing formation to move the fluidtowards and into the well'unimpeded by bottom-hole pressure or back pressure in the 15 same.

Other things being equal the production of. fluid of a well will vary between zero when bottom-hole pressure in the same is at its maximum and equals stabilized formation pressure; and 20 maximum production of fluid when bottom-hole pressure is entirely removed. It follows then' eduction tube. This is accomplished without dis- 35 charging any. portion of the slug of liquid so riding, nor reduci'ngits volume during the major part of its up-stroke until the upper end of the liquid slug reaches the discharge openingof the eduction tube. The discharge of the liquid by 40 the plunger is then begun and thereafter con tinued until the plunger reaches the end of its stroke. The plunger is propelled by gas in the eduction tube under the same. Said gas may be produced currently from the producing forma-. 45 tion with the oil, or from an independentsurface source of supply, or by the former if inadequate supplemented by. the latter.

In such plunger-lift devices installedlin even only moderately deep wells the time consumed in a plunger round trip is considerable and consequently the number of .such round trips per unit of time is so reduced that the slug of liquid required to be handled per round trlplof the 55 plunger is oi considerable height andits static wells is required or desired,- bottom-hole pressure pressure and. accordingly the required plungerpropelling --gas pressure are correspondingly great. Under favorable 'conditions with such plunger-lift apparatus the plunger propelling gas pressure which must be maintained in the well casing outside of theeduction tube above the operating liquid level in the well is from 25% to 50% greater than" the static pressure of the column of liquid riding on top of the plunger". To this increased pressure must be added, to determine full bottom hole pressure, the static pressure of the columri of liquid from the operating liquid level in the well outside of the eduction tube to the bottom of the hole. This bottomhole pressure is continuous and without material variationdn pressure during the operation of the plunger-lift. This excessive bottom-hole pressure exerts a correspondingly high back pressure against the fluid in the producing formation adjacent the well bore and reduces to this material extentthe moving effect of the fluid pres-' sure in the outlying producing formation. This accordingly reduces materially and seriously affects the production of fluid of the well.-

It is an. object of my invention to provide a we'll-pumping apparatus which will retain all the' advantages of the regular single stage plunger-liftdevice and at the same time utilize to a material degree the lifting power of -'the formation gas currently'produc'edvrom the producing formation with the liquidto be removed I from the .well, without subjecting the well bore and the adjacent producing formation to ob-" jectionably. high bottom-hole pressure, but with 1 propelling gas soulow in pressure as to render negligible. the resulting back pressure acting against the fluid flowinginto the -well bore.

It is also an object of my invention to provide amethod ofand apparatus for operating wells.

whichwill combine low lifting cost with the 49' highest potential production of the fluid sought.

Itis another object to provide a well pumping apparatus and method for and of operating wells which byreason of its flexibility can by simple adjustment on the ground be readily adapted to meet any conditions of well, formation and fluid. It is a further object to provide a fluid-removing apparatus which will be autornatic in the complete performance of its regular operating functions or cycles and require a minimum of 50 operating attention. 7.

It is a further object to provide a fluid-removing apparatus which while removing the liquid: from the pumping depth in the wellwill also remove and/or effect the escape or release 01"55' 7 a fluid-removing apparatus which while removing the liquid and formation gas from the well will reduce bottom-hole pressure in the well to a practical operating minimum favorably comparable with that efiected by the most efficient of other such devices.

I have illustrated the invention as appliedto a pumping well equipped with my device for raising the oil and gas from the pumping depth to the surface of the ground. I

In the drawings herewith:

Fig. 1 is a central longitudinal section through the extreme upper portion of a well installationembodying my invention. This, entire portion is above ground, More correctly speaking this is the extreme upper portion of the upper or secondary lift.

Fig. 2 is a similar section through anintermediate portion of the same well installation. It shows the extreme lower portion of the secondary lift. It adjoins that shown by Fig. 3 on the line A-B. 1

Fig. 3 is a similar section through another intermediate portion of the same well installation. It shows the extreme upper portion of the lower or primary lift. It adjoins that shown by Fig. 2 on the line AB.

Fig. 4 is a similar section through the extreme lower portion of the same well installation, which is also the extreme lower portion of the primary lift.

Fig. 5 shows an alternative arrangement in which the string of tubing which extends from the gas admission valve housing to the top of the well and which forms and separates the pressure gas passageway from the casing space, is omitted compartments.

. ing compartment and the low well pressure above the liquid in the well bore or cavity would bein the lower compartment below the packer. A separate gas pipe may be strung from the packer through the upper casing compartment to make communication between the surface and the lower casing compartment, if desired.

Fig. 6 is a fragmentary section on a larger scale through a part of the lower portion of the secondary lift shown by Fig. 2. It shows in greater detail of construction the gas admission valve which admits pressure gas procured from a surface sourcejto the annular liquid-receiving, storing and transferring chamber after said chamber has'been charged with liquid discharged into it by the several consecutive strokes or cycles of the primary lift plunger.

, Like parts shown in the several figures have the same reference numbers. 7

Thewellcasing I usually extends from the top of the well to a point above the producing formation where it is cemented. 2 is the primary smooth bore eduction tube and extends within the casing from near the bottom of the wcllbore to.a primary lift discharge chamber l8. 'Ihis chamber and the liquid-receiving, storing and transferring chamber are located at as great a predetermined elevation or height in the well as will permit of the most advantageous utilization f( r liquid lifting purposes, of the maximum quantity of formation gas available and currently produced. The lift must be done without reducing the number of round trips of the primary lift plunger per unit of time to such a degree as to excessively increase the height of the slug of liquid carried on the primary plunger per trip and consequently the plunger propelling gas pressure in the casing with the resulting excessive bottom-hole pressure. In other words, in practice the height or elevation of the top of the primary eduction tube should be a compromise between the degree or extent of the utilization of formation gas for liquid lifting and the maintenance of the reasonable minimum bottom-hole pressure. 3 is the secondary smooth bore eduction tube and extends upwardly from the primary discharge chamber l8, at an elevation slightly above the upper end of the primary eduction tube, to the top of the well above ground. The diameter of this secondary eduction tube should preferably be larger than that of the primary eduction tube to facilitate the withdrawal of the discharge valve and valve seat and the plunger of the primary lift without removing the secondary eduction tube from the well.

tion tube when it is desired to increase fluid lifting capacity without increasing the diameter of the primary eduction tube because ofwell bore or casing diameter limitations at the lower end of the well.

4 is a string of tubing extending from the gas admission valve housing 8 to the top of the well. It forms between its inside diameter and the perimeter of the secondary eductiontube 3 an annular passage 5 through which pressure gas from a surface source'of supply is conveyed to the gas admission valve, from and by which it is delivered to the chamber I to displace and raise the liquid from same into the primary lift discharge chamber l8 and secondary eduction tube 3 to load and propel the secondary plunger 25. The

- tube 4 also forms, between its perimeter and the inside diameter of the casing |,an annular passage 6 through which formation gas in excess of that which passes through the eduction tubes 2 and 3 to the surface may escape to the surface, or

Or its diameter may be still further increased over that of the primary educthrough which a supply of pressure gas from a surface source may be conveyed to'the well bore or cavity I2 above the liquid level in same for liquid lifting purposesin the primary lift when formation gas is of insuflicient quantity.

The space I, as seen in Fig. 3',is a double legged U shaped liquid-receiving,.storing and trans ferring chamber formed by the tubular members- 8 and 9 and the perimeter of the primary eduction tube 2 andv the bottom coupling I 0. The inner and outer legs 1 are connected together just above coupling In by perforations I l in the lower end of member 9. This chamber 1 is located so that the major portion of its volumetric capacity lies at an elevation in the well below the elevation of the primary lift discharge chamber l8, in order that pressure in chamber 18 opposing the discharge of liquid and gas from the primary eduction tube 2 will not be materially affected or varied by the several subsequent discharges of the primary plunger until chamber 1 is fully charged. Liquid then builds-up in discharge' I 9,160,291 it up further and until said built-up column in I8 and 3 has reached the predetermined height sufficient to actuate the opening of gas admission va'lve 3|. Opening valve 3| admits pressure 1 space, forming an annular passageway connecting the upper casing space or passage 6 with the lower casing space l2.

The primary lift plunger l travels in the pri-, mary eduction tube 2 from the pumping depth in the well to a point near the upper end of said tube. A cushion stop I3 is provided at the lower end of its travel. Against this stop the stem of the valve l4 in the plunger will contact to close the valve. At the up er end of its stroke the plunger discharges its superposed slug of liquid through a primary discharge valve seat l6 and upwardly opening valve 11 to primary discharge chamber l8, ,Here the liquid spills over and down into the inner leg of chamber 1 at the level l9. From here it flows into the outer leg of chamber 1 through perforations ll. .Gas above the plunger passes on up through the secondary eduction tube 3 and out at the'surface. The valve seat, I1 is shown as screwed into the'.upper end of the eduction' tube. Other means of attachmentmay be used.

I nular cushioning space. formed by a part of the' The. valve H in the plunger is opened near the "upward limit of its travel by contact with the plunger stop 20. This allows the propelling gas below the plunger and some of the gas from the well bore to escape upwardly to the surface through tube 2, valve I1, chamber l8, tube 3,

openings 2| and flow line 22.

The secondary stage of my device receives the fluid from the primary stage. The secondary lift plunger has a valve 26, like the valve M of the primary plunger. Both plungers, l4 and 25, are of the usual construction now in use. A cushion stop 21 forplunger 25 is formed upon the supporting post 28 mounted on the upper end of valve seat l6. 'This stop engages the plunger valve 26 and closes it as the plunger approaches its lowest or loaded position. Projections 29 .on

the upper and lower surfaces .of the valve II are provided; Those on the lower surface engage torsionally with the ribs in the seat l6. 'Those on the upper surface engage with fingers, .straddling the cushion stop 21. of a setting tool which may be used to screw the valve seat l6 into position in the upper end of eduction tube 2; or'to unscrew and withdraw said valve, seat and the primary plunger I5 from the well, without removingthe secondary eduction tube 3. 38 is an anvalve seat l6 and the interior surface of the eduction tube 2. The upper erid of the plunger |5 as'it approaches the upper end of its stroke enters this cushioning space and the gradual rea lease of fluid from the same brings the plunger to rest gradually without harmful impact.

- 3| is an automatic gas admission valve of the annular sleeve valve type. It moves in an' an- A valve is'partially open into the upper end of the outer leg of the chamber 1 formed between the tubular members 8 and '8. is an annular pas-' 3 sage formed between the perimeter of tube 3 andthe inside diameter of the housing member 32. It connects the pressure gas supply passage 5 with perforations or ports 36, which in. turn make communication between passage 35 and the hous- 5 ing space in which the sleeve valve operates,'when the perforations 36 are uncovered by said valve.

The totalcross sectional area of perforations 36 and/or of passage 35, should preferably be restricted to the minimum actually required to pass, 10

with-some wire-drawing, the quantity of pressure gas required for propelling the secondary plunger at the required velocity. The cross-sectional area v of the opening 34 between the valve housing space -31 and 38 to close the gas admission valve 3| again st reduced pressure in the housing space under it. 31 is a sleeve valve spring. It resists the opening of valve 3| from its closed position as shown, to its initial opening position of perforations 36 and to theiull open position of the valve. It acts to close said valve from itsfull open position to its full closed position against reduced pressure in chamber 1. 38 is another sleeve valve-spring which opposes the openihg of said valve'by pressure gas from the surface source from the initial opening positionof perforations 36 to the.fu1l open position of the valve. This spring 38 also acts in concert with spring 31 .to move valve 3|, against reduced pressure-under it, from its full open position to that position when it just closes perforations 36. From this position spring 31 alone completes the closing of the valve against a still further reduced pressure .in chamber 1 due to the continued release of plunger propelling gas from eduction tube 3.- I have omitted the spring 31 from Figs. 2 and 5 .for clarification purposes. 48 are pressure relief pressure, from the former into the latter. 4| is I a cushioning recess into which the upper end- 50 of the sleeve valve 3| enters as it approaches its top position to cushion the stopping of same. The space between 'the housing 33 and the casing may be sealed at 42 by a gas packer shown in Fig.5 placedabove-the gas admission valve housing to separate'the casing space into upper and lower compartments when the string of tubing 4 is omitted and the upper compartment used to convey pressure gas from the sur-" face.source to the gas admission valve through passage 35 and perforations 36. i 43 is a casing head secured at the upper end of casing-l. 44, is a gas supply pipe through which a regulated supply of reduced pressure gas from asurface source is fed to the casing space to make up any deficiency in quantityof formation/ 'gas to operate the primary plunger lift; or to supply pressure gas to the gas admission valve 3| ,when string of tubing '4 is omitted. 45 is a gas discharge pipe connected with the ,field gas gathering systemfor discharging and conserving any excess of formation gas from the casing space not used or released by the plunger lifts. 46 is a gassupply pipe for furnishing regulated A pressuregas from a surface source through pas sage to the gas admission'valve 3| housing space and chamber'l.

J 41 is a gate valve used for trapping suchparts as plungers when their removal from the well is required. '48 is a buffer of resilient material for cushioning the secondary plunger should it I come to the surface unloaded. 49 is a cap for closing theupper end'of the secondary eduction tube 50. 5| is an, outlet pipe closed normally by a valve 52. g .3.

A plunger-retaining'latch 24and its automatic control mechanism are secured u'po'rf'the extension head 23. The latch bolt 24 is extended into an opening in the side of 23 and has a-s'temfl projecting outwa rdly through the wall of the bracket 54 to connect at 55 to a bell-.crank lever pivoted upon a support at 55. The outer arm of the lever engages the rod 5] upon a piston 58 movable within a cylinder 59 and held resiliently downward by a spring 50. The cylinder 59 has a port below the piston 58 to which is secured a pipe 5i which connects at its other end with e port52 in. the tube extension head 2:.

There is a check valve ea in this line allowing passage offluid fr -.1: to the: cylinder.- v1 providea by-pass'aroundgthecheckvalve 52 by way f a'small pipe 64 in which is a handadjusted f choke valve 65 for regulating. the time during which the secondary plunger is held in its upper position. Qthersuitable automatic means may be substituted for retaining the plunger in its upper position and releasingsia-l It will be wardly to retract latch 24 and release the plung- 5 follows:

understood that t e latch 24"will be moved to plunger engaging position by the pressure through pi es: of fluid being forced upwardly by the plunger. When this pressure is later 'released, the spring will move piston 58 backdowner. The time of release may be regulated by valve 55 in pipe 54 which controls the passage of fluid from, beneath the piston 58.

. The operation of the method-and deviceis as -The well has been-shut down'and is to be started up again. The secondary plunger was permanently latched in its highest operating position before the well was shut down and is in that position. Primary plunger I5 is in its low position on top of cushion stop 13 with its valve l4 shut. Liquid has risen in the casing space l2 and in primary eduction tube 2 and its surface level is at the headed-upfor standingle'vel elevation.

Pressure gas froma surface source .ls admitted by hand into casing space 5 from pipe 44 and builds up gas pressure in the well bore and' casin'g space l2 above the liquid in same and displaces liquid intothe' primary eduction tube 2 and moves primary plunger l5 .to its highest po-' mit gas admission valve 3| to be opened by the pressure' of-eitlfie column of liquid vin eduction v 1 Pressurefgas from the surface .isthen i Pressure gas is then passage 5 and gas admission valve II is thus opened full and the pressure gas passes on into the outer leg of chamber 1 and displaces the liquid from the outer and inner legs of same and raises it through chamber l8 up into the secondary eduction tube 3. As soon as pressure gas breaks through the liquid column in 3 to the surface the secondary plunger 25 is released by hand and falls to its low position underneath its load of liquid and plunger valve 26 shuts. Secondary plunger 25 then makes its up-stroke and .as it approaches the end it discharges the liquid above it, propelled by pressure gas still admitted by valve 3|. When the secondary plunger 25 reaches its top position in tube 3 and has discharged the fluid above it, latch 24 engages and holds it in that position. Propelling gas from 3 under the plunger and from discharge chamber I 8 and from chamber 1 then escapes through perforations 2| into flow line 22 and gas pressure in them is reduced which automatically causes the gas admission valve 3| to close, discontinuing the inflow of pressure gas.

' .At this stage of the initial operation both the primary-and secondary lifts have each completed one discharge of liquid. The secondary lift is ready to receive regular cyclic discharges of liquid from the primary lift and lift them to the surface and discharge them and continue cyclic operations automatically. The primary lift however, after making only one discharging cycle, is not ready to continue operating automatically because liquid and gas conditions in the well space l2 andoadjacent producing formation have not yet stabilized in these respects: First; the flow of formation gas into the well bore has not even approached what it will normally be under continuous operation and second; only a small part of the accumulation of liquid in the well from the shut-down period has been removed from space l2 and primary eduction tube I 2 and the adjacent producing formation; and besides, the oil is more or less inert.

Before the conditions are stabilized and the well isin shape for continued automatic operation of the complete lift, it may therefore be necessary to repeat several times'the initial cycles largely by hand control, until it is ready for automatic control operation, which will then be as follows:

Secondary plunger 25 .is being held at the top by the latch 24. Gas has been discharged and gas pressure released and practically all liquid has been removed from the entire secondary lift and from the chamber I of the primary lift.

The gas admission valve 3| has closed and as pressure has been removed from above it the primary discharge valve I'l opens and releases gas from the primary eduction tube 2 above the slug of liquid on top of the primary plunger l5.

This gas escapes through valve seat" It, valve l1,

chamber I 8, eduction tube 3, perforations 2| and flow line 22.

Formation gas and/or pressure gas has builtup pressure in casing space l2 and has depressed. the liquidlevel in same until it uncovered the extreme lower end of eduction tube' 2, and thus permitsgas from space l2 and the adjacent producing formation to enter eduction tube 2 under the primary plunger l5 and drop and displace liquid therefrom. The primary plunger then resumes its upward stroke and first displaces the superimposed 'free gas and then discharges the liquid slug through primary discharge seat and valve-fl. *and-i'l -into chamber In. The superimprimary plunger I and causes fluid to flow into- I 2,160,291 posed gas passes out through eduction tube 3 and perforations 2| and flow lines 22. The liquid spills over into the inner leg and through perforations I I intothe outer leg of chamber 1. The

propelling "gas under plunger IS in the primary eduction tube 2 passes on through plunger valve -|l, discharge seat and valve l6 and H, discharge chamber l8, into eduction tube 3 and out of the .well throughperforationsZl and flow line 22. This reduces gas pressure in eduction tube 2 under the portion of eduction tube 3 is also charged up to the predeterminedelevation, at which the gas admission valve 3| is actuated, initially uncovering perforations 36 and admitting pressure gas from passages 5 and 35 to the housing space under the valve 3 I. This opens it to the full open position and admits pressure gas to the outer'leg .of chamber '1 on top of the liquid in same, displacing the liquid in this leg and'the liquid in.

the inner leg'of chamber land transferring it into the lower portion of the secondary eduction tube 3 to the plunger liquid-loading elevation in same.- Thesecondary plunger has been automatically unlatched and falls through the liquid and comes torest on cushion stop 21 which closes its valve 26 and said plunger then makes its upstroke, propelled by pressure gas still fed past thegas admission valve 3|. As this secondary plunger rises on its up-stroke it lifts intact the superimposed slug of liquid; the stratum of free gas above the liquid slug being displaced through perforations 2| and flow line 22 as the :plunger rises, until the top of the liquid slug reaches the perforations 2| when the discharge of liquid from eduction tube 3 begins. secondary plunger reaches the end of its stroke and completes the liquid-discharging minor portion of its up-stroke. The latch 24 then engages said plunger and the propelling gas, from the eduction tube 3 'under the plunger escapes through perforations 2| and flow line 22. The reduced pressure resulting, in eduction tube 3 and in chamber 1 and in the housing space under the gas admission valve 3|, permits valve springs 31 and 38 to close the valve 3|. Pressure is then exhausted from eduction tube 3 and chambers I and I8 and the primary lift resumes its automatic operation. The cycles are continuously repeated.

What I claim as new is:

1. A plunger lift device including an eduction tube, a primary stage therein, a freely moving plunger in said primary stage, a standing valve at the upper end of said primary stage, an interjstage liquid reservoir in or around the upper portion of said primary stage below said standing valve, an upper secondary stage in said eduction tube, a second freely moving plunger above said standing valve in said secondary stage, there being openings into said tube below said second plunger, a, sleeve valve closing said openings, means to conduct gas or air under pressure from the surface to said valve, said valve opening in response to the head of liquid in said eduction tube above said standing valve. 2

It continues until said 2. A plunger lift apparatus including a tubing, a tubular valve housing thereon comprising two spaced pipes including an annular valve chamber between them, the inner wall of said chamber being formed 'with perforations adjacent its lower .end, a sleeve valve controlling said .openings and closing the lower end of said chamber, means to hold said valve resiliently downwardly into closed position, a fluid receiving chamber below said valve chamber, a primary eduction tube spaced inwardly from saidchamber and extending below the same, the space between'said eduction tube and said fluid receiving chamber being connected to said chamber by'openings at the lower end of said chamber, a freely moving plunger in said primary eduction tube, a stop for said plungerat the upper end of said primary eduction tube, a standing valve above said stop, a'second eduction tube above said standing valve, a plunger freely movable therein, and means to introducegas under pressure past said sleeve valve to said second eductiontube below said secondplunger responsive to the head of liquid in said second eduction tube;

3-. A plunger lift apparatusincluding a tubing, a tubular valve housing thereon comprising two spaced pipes includingan' annular valve chamber between them, the inner wall of said chamber I being formed with perforations adjacent its lower end, a sleeve valve controlling said openings and closing the lower end of said chamber, means to hold said valve resiliently downwardly into closed position, a fluid receiving chamber below said valve chamber, a primary eduction tube spaced inwardly from said chamber and extending below the same, the space between said eduction'tube and said fluid receiving chamber being connected to said-chamber by openings at the lower end of said chamber, a freely moving plunger in said primary eduction tube, a stop for said plunger. at the upper end of said primary eduction tube, means to prevent the entrance of fluid from above to saidprimary eduction tube whereby liquid may be accumulated in said fluid receiving chamber and about said eduction tube by a plurality of consecutive stroke cycles of the primary plunger, a second eduction tube above said primary eduction tube, a freely movable plunger therein, ;means to discharge pressure gas into said second eduction tube past said sleeve valve when the head of liquid in the same from the primary lift has reached a predetermined amount,

said sleeve valve being closed when said second plunger has been raised to the surface and said pressure reduced.

4. In a plunger lift device, a secondary eduction tube, a primary eductic tube extending from the liquid in the' well pwardly into said. secondary eduction tube and. connected with thelower end of said secondary eduction tube,- a

plunger freely movable in said primarytube, a

standing valve at the upper end of said primary tube, a second plunger in said secondarytube above said standing valve, a stop for said second plunger, on said valve, an annular-passage about said secondary eduction tube for pressure gas or air, from the surface, a 'valve in said passage controlling the entrance of gas therefrom to said tube, said valve .being opened in response to the liquid pressure in said secondary eduction tube.

5. In a plunger lift well-pumping apparatus, an eduction tube, a primary stage therein, an inter.- stage liquid reservoir in or around the upper end of said primary stage, a secondary stage, a valve controlling admission of fluid from said primary to said secondary stage, a freely moving plunger in each of said stages, the secondary stage plunger lifting superimposed in one stroke-cycle substantially the same quantity of liquid lifted by the plural consecutive stroke-cycles of the end thereof, and a higher lift larger stroke secondary stage extending from near the upper end of the primary stage to the surface of the ground, a 'freely moving plunger in each of said stages, means to exert gaseous fluid pressure below said primary stage plunger and -lift the liquid from near the pumping depth into said interstage reservoir and the lower end of the secondary stage, t

means to introduce below said secondary stage plunger gaseous pressure fluid from a surface source, and a fluid pressure responsive valve controlling the admission of gaseous fluid to said secondary stage.

CLARENCEN. SCO'I'I. 7 

